Metallic pigments in general, and aluminum pigments in particular are widely used in the coating industry to produce finishes of the type which have a metallic luster. The procedure generally used at the present time to produce a colored finish with a metallic luster is to disperse both a metallic pigment and a transparent colored pigment in a suitable vehicle. Such dispersions have achieved wide acceptance as automotive finishes wherein a plurality of interesting colors having a metallic luster have become increasingly popular.
A previously recognized problem has been to provide a commercially acceptable procedure for economically coloring metallic pigments. Heretofore, attempts at coloring aluminum flake pigments have been tried by prior workers in the art, using a precipitation of iron oxide onto the aluminum pigment surface. Although this method produces a flake with a gold color, the procedure is rather complicated.
Another previously attempted solution was coloring metallic pigments as disclosed in U.S. Pat. No. 4,328,042 wherein the vapor deposition of iron penta-carbonyl onto an aluminum flake surface is taught. The subsequent oxidation of the iron penta-carbonyl to iron oxides and carbon dioxide then produces a colored flake. However, the color of this flake is dependent on the conditions of processing and thickness of the iron oxide layer.
In U.S. Pat. No. 4,158,074, a process for coloring aluminum powder is disclosed which includes immersing finely divided aluminum in a weak alkali solution containing a specified metallic salt and an aliphatic amine and then separating the aluminum from the solution. In U.S. Pat. No. 5,037,475 a process for coloring metallic pigments is taught that includes treating the metallic pigments with a thermally polymerized carboxylic acid having at least one double bond and at least two carboxylic acid groups, then adsorbing a colored pigment onto the treated pigment; optionally coating this product with a polymer comprised of a polymerizable unsaturated carboxylic acid and a monomer having at least three polymerizable double bonds.